Research On Micro-Arc Oxidation Film And Electro-Chemical Corrosion Of AM60 Magnesium Alloy

Magnesium alloy has a series of advantages such as rich resources,good damping,high thermal conductivity,strong magnetic shielding ability and easy recovery and so on,it is widely used in the fields such as transportation,electronic industry,medical equipment and military industry.However,the standard potential electrode of magnesium alloy is very low,which leads to poor corrosion resistance of magnesium alloy and severely limits its application.The corrosion resistance of magnesium alloy can be greatly improved by the micro-arc oxidation technology.In this paper,AM60 magnesium alloy was selected as the research object,and the process parameters were optimized by single factor experiment with the low-voltage micro-arc oxidation technology.The section morphology and phase composition of the film were analyzed by SEM and XRD.The growth characteristics and corrosion behavior of the film were studied by using the method of electro-chemical and morphology analysis,and the correlation between the electro-chemical corrosion performance and the structure of the micro-arc oxidation film was established,the problem of poor corrosion resistance of film layer in traditional micro-arc oxidation was solved.The results are as follows:(1)The micro-arc oxidation film is mainly composed of MgO phase and MgF2 phase.The micro-arc oxidation film is composed of dense layer and loose layer.The relationships among KF concentration,KOH concentration,voltage,treatment time,treatment liquid temperature and film thickness were obtained by single factor experiment.(2)When the thickness of the film layer is less than 10 ?m,the self-corrosion voltage increases with the thickness of the film layer,and the self-corrosion current decreases with the thickness of the film layer.When the thickness of the film is more than 10?m,the self-corrosion voltage and self-corrosion current are basically unchanged with the thickness of the film.(3)When the thickness of the film layer is less than 10?m,the impedance value of the dense layer and the loose layer increases with the thickness of the film layer.The impedance value of the dense layer increased significantly,and the value was much higher than that of the loose layer.When the film thickness is more than 10?m,only the impedance value of the loose layer increases slowly with the film thickness.The thickening of dense layer mainly occurred in the early stage of micro-arc oxidation,while that of loose layer occurred in the whole process of micro-arc oxidation.(4)When the thickness of the film is more than 10?m,the self-corrosion voltage and self-corrosion current of the film are basically unchanged.Therefore,the most reasonable film thickness is 10 ?m,and the corresponding process parameter is:The concentration of KF is about 370 g/L,The concentration of KOH is about 147 g/L,voltage is about 95 V,the treatment time is about 40s and the treatment temperature is about 22 ?.In this experiment,the film with strong corrosion resistance was successfully prepared by micro-arc oxidation technology,and the corrosion resistance of AM60 magnesium alloy was improved.The self-corrosion voltage of the film reaches-0.415 V,which is nearly 1.5 V higher than that of the matrix.The self-corrosion current density reached 3.560×10-7 A/cm2,which was 3 orders of magnitude lower than that of the matrix;Impedance values of 1556 ? loose layer,the 3 orders of magnitude higher than that of matrix;Dense layer impedance value reached 1.398×107 ?,the seven orders of magnitude higher than that of matrix.